DESCRIPTION: (adapted verbatim from the investigator's abstract) A breast cancer in one patient may look identical to that of a second patient, but the first patient may die of the disease within a few years, while an identically treated second patient never recurs. Currently 2/3 of patients with breast cancer show no evidence of lymph node metastases at presentation. Many of these patients could be adequately treated without systemic (chemo) therapy if there were specific biological markers that could assess metastatic potential. We postulate that MET protein expression may be such a marker. The Met protein regulates signals for decreased cell adhesion, increased cell motility, increased tumor invasiveness and increased cell growth rates. In a pilot study, we have found that Met expression in invasive cancer cells is associated with significantly decreased survival (from 89% to 52% at 5 years) and, by multivariate analysis, that this finding is independent of lymph node status and size, the two best current markers of prognosis. We propose a twofold approach to test the hypothesis that expression of Met is an indicator of aggressiveness and metastasis in breast cancers. We propose to 1) define the mechanism by which Met expression leads to poor outcome; and 2) assess the prognostic value of this marker in a both retrospective and prospective studies.